In general, a liquid crystal panel is suitably used in a display for a liquid crystal television or a personal computer serving as a display apparatus, and it has remarkably widely been used in recent years. In the liquid crystal panel, out of necessity in management during production or necessity in maintenance after shipment, various types of information such as serial information and information on use thereof are marked. Laser marking is normally suitably utilized for this marking, and the various types of information described above are marked during a production process by irradiating a glass substrate for a liquid crystal panel, which is a component of the liquid crystal panel, with laser beams.
As a method of marking various types of information in a glass substrate for a liquid crystal panel by utilizing laser marking, for example, a marking method by irradiating an ITO (Indium Thin Oxide) film formed on a surface of a glass substrate with laser beams (see Japanese Patent Laying-Open No. 6-51328 (Patent Literature 1)), a marking method by irradiating an orientation film formed on a surface of a glass substrate with laser beams (see Japanese Patent Laying-Open No. 10-278422 (Patent Literature 2)), a marking method by irradiating a metal film formed on a surface of a glass substrate with laser beams, and the like have been known.
Among these, in the marking method by irradiating a metal film formed on a surface of a glass substrate with laser beams, specifically, marking is provided in the glass substrate by providing a marking pad by forming a metal film in a peripheral portion of the glass substrate not serving as a liquid crystal display portion, irradiating this marking pad with laser beams, and thus forming a through hole in the marking pad. It is noted that various types of information thus marked are marked in the glass substrate as a two-dimensional data code with the information being data-matrixed, and the information is read by using any of a reflection camera and a transmission camera.